Process for Metal Seperation Using Resin-in-Pulp or Resin-in-Solution Processes

ABSTRACT

A process for the treatment of solutions or slurries containing dissolved metals comprises the steps of (a) contacting the solution or slurry with an ion exchange resin that selectively removes one or more dissolved metals from the solution or slurry wherein the solution or slurry and the resin are introduced into a vessel or column via sub-surface means, (b) separating loaded resin from the solution or slurry, (c) eluting the one or more metals from the loaded resin with an eluting agent, (d) separating the eluting solution containing eluted metal ions from the resin; and (e) transferring regenerated resin from step (d) back to step (a).

BACKGROUND TO THE INVENTION

The present invention relates to a process for metal separation using resin-in-pulp (RIP) or resin-in-solution (RIS) processes.

BACKGROUND TO THE INVENTION

A number of mining and downstream processing technologies applied to run of mine ores result in the formation of soluble metal containing solutions and pulps (slurries). Some of these solutions or pulps arise from intentional processes (such as leaching and other mineral processing and hydrometallurgical processing technologies) while others may arise from water run-off from tailings dams, waste rock dumps and the like, and may accumulate in abandoned mining pits or be discharged into the surrounding environment.

Solutions and slurries produced by leaching or other hydrometallurgical processes typically contain one or more soluble valuable metals (in the form of dissolved metal ions), together with one or more soluble impurity components. A number of processes are available to separate and recover the valuable metals. These include precipitation, solvent extraction, adsorption and use of ion exchange resins. In the case of ion exchange resins, it is possible to use clarified solutions (known as resin-in-solution) or to directly treat the pulp or slurry (known as resin-in-pulp).

Other solutions containing dissolved metal ions may be formed due to acid mine drainage or acid rock drainage. These solutions represent a significant source of environmental damage and degradation.

In general, ion exchange processes (such as resin-in-pulp and resin-in-solution processes) are best applied to solutions and slurries that have relatively low soluble metal concentrations and/or contain soluble metals that have a high intrinsic value. Examples of such metals having a high intrinsic value include gold, uranium and platinum group metals. For example, resin-in-pulp and resin-in-solution processes are frequently used in the processing of gold ores and uranium ores.

Resin-in-pulp and resin-in-solution processes are not normally used for the treatment or recovery of base metals. In the recovery of base metals, the concentration of the dissolved metal is normally much higher than would be experienced in the recovery of gold or uranium. Due to the high concentration of dissolved valuable metal, the ion exchange resin has to undergo much more frequent cycling through loading with the desired metal ions and regeneration by removing or stripping the metal ions from the resin. More frequent cycling of the resin normally results in more rapid attrition or breakdown of the resin. This, in turn, leads to increased costs for fresh or replacement resin.

It will be appreciated that there are a number of processing challenges in a commercial application of ion exchange technology. First and foremost, the solid resin needs to be physically transferred in a manner that optimises its efficiency and selectivity for metal removal/recovery and in a manner that minimises the physical and chemical degradation of the solid ion exchange resin through various means such as attrition and/or osmotic shock. This applies to each of the three major steps involved in ion exchange processes, namely loading (in which the resin becomes loaded with the valuable metal by contacting fresh or regenerated resin with the solution or pulp containing the dissolved valuable metal), washing (in which excess or adherent solution or slurry is washed from the resin) and elution (in which the resin is contacted with a solution that removes the valuable metal from the resin to thereby regenerate the resin and recover the valuable metal into a more concentrated stream that contains less impurities).

Excessive resin attrition can represent a significant operating cost through the need to regularly replace the resin. In addition, metal losses are associated with broken resin beads that are subsequently lost from the processing circuit.

Throughout the specification, the term “comprising” and its grammatical equivalents should be taken to have an inclusive meaning unless the context of use indicates otherwise.

The applicant does not concede that the prior art discussed in the specification forms part of the common general knowledge in Australia or elsewhere.

BRIEF DESCRIPTION OF THE INVENTION

In a first aspect, the present invention provides a process for the treatment of solutions or slurries containing dissolved metals comprising the steps of:

a) contacting the solution or slurry with an ion exchange resin that selectively removes one or more dissolved metals from the solution or slurry, said contacting comprising introducing the solution or slurry and the resin into a vessel or column, wherein the resin is introduced into the vessel or column via sub-surface means,

b) separating loaded resin from the solution or slurry;

c) eluting the one or more metals from the loaded resin with an eluting agent;

d) separating the eluting solution containing eluted metal ions from the resin; and

e) transferring regenerated resin from step (d) back to step (a).

In some embodiments, the process further comprises washing the loaded resin to remove entrained solids, solution or slurry prior to step (c);

In the process of the present invention, step (a) results in the resin being introduced into the vessel or column below the surface of the solution or slurry in the vessel or column. This is advantageous in that it assists in mixing and contacting the resin with the solution or slurry. Further, the amount of agitation required to mix the resin with the solution or slurry is minimised which, in turn, minimises attrition of the resin caused by such mixing.

When working with slurries having a high solids content or working with slurries or solutions having a high viscosity, there is a tendency for resins to float on the surface of the slurry or solution. Utilising sub-surface introduction of the resin also tends to overcome this problem, which again minimises the amount of agitation required to mix the resin with the slurry or solution.

In some embodiments of the present invention, the slurry or solution may be subjected to a pre-treatment that removes oversize particles and other contaminants therefrom prior to contacting or mixing the slurry or solution with the resin. The pre-treatment step may comprise any known treatment step that can remove oversized particles from slurries or solutions. Examples include screening, settling, sedimentation, clarification, hydrocyclones, centrifuging and the like. It is envisaged that pre-screening is the likely treatment to be used in commercial applications of such embodiments of the present invention, but other pre-treatment steps also fall within the scope of the present invention.

The pre-treatment step to remove any oversized particles and other contaminants stops oversize particles and other contaminants from accumulating in the process circuit. Furthermore, oversize particles and other contaminants tend to increase the attrition of resin particles as the oversize particles may act like grinding media. Therefore, removal of oversize particles and other contaminants will act to minimise attrition of the resin particles.

The mixing of resins with pulps has historically been achieved by means of air mixers, such as air mixed pachucas. Whilst physical attrition of the resin beads may generally be at an acceptably low level, the operating costs associated with provision of the air supply are often unsustainable in economic terms. The present inventors have found that mechanically agitated mixers may be used in embodiments of the present invention. However, it is preferred that particular attention be paid to the design of the agitators and in particular, it is desired that the maximum tip speed of the mixing blades be sufficiently low that physical attrition of the resin beads is minimised. Accordingly, in embodiments of the present invention, it is preferred that low speed and/or low shear mechanical mixers be used to mix the resin with the solution or slurry. The desired tip speed of the agitators will depend somewhat on the strength and attrition resistance of the resin being used. The agitator design and tip speed are desirably controlled such that a balance between avoidance of “sanding out” (which results in the heavier particles in the pulp settling out) and excessive agitation of the resin is achieved. In some embodiments, with the tip speed of the agitator may be less than 4.0 m/sec, more preferably less than 3.8 m/sec.

In some embodiments of the present invention, pulps and solutions to be treated may require the addition of specific reagents to adjust the pH of the solution/pulp to ensure that the target metal(s) remain in solution while at the same time ensuring that the ion exchange resin is operating within its optimal pH range for metal uptake. In addition, it may be appropriate to adjust the operating pH to remove potentially interfering non-target soluble metal ions by in-situ precipitation. A typical example is the removal of soluble ferric ions by increasing the pH of the solution/pulp to a value typically in the range of about 2.8 to 3.8.

In those cases where efficient separation and recovery of valuable metals requires oxidation of ferrous iron and subsequent precipitation of ferric iron by adjustment (neutralisation) of the pH, the normal practice has been for this step to be carried out prior to introduction of the solution and/or slurry to the ion exchange circuit. The present inventors have discovered, however, that this overall step can be conducted within the ion exchange circuit itself in embodiments of the present invention. In other words, in these embodiments, the inventors have found it unnecessary to incorporate a separate oxidation/precipitation step ahead of the ion exchange circuit. This results in considerable capital and operating cost benefits.

In embodiments which require the addition of reagents to modify the pH to the optimum range, which typically involves addition of a neutralising agent, addition of the neutralising agent generally causes solids to form in the solution and/or increase the percentage of solids when using the RIP mode of operation. Where limestone or other solid neutralising agent is used as the acid neutralising agent, it is preferable to screen out any oversize particles before the pH adjusted solution or pulp is forwarded to the ion exchange circuit. If this oversize material is not removed by this pre-screening step then there may be problems encountered with the resin screening process itself.

Indeed, embodiments of the present invention that include the addition of solid reagents or solid reactants to the process may further include a step of treating, such as screening, the solid reagent or solid reactants to remove oversized material therefrom prior to mixing the reagents or reactants with the solution or slurry.

The present invention encompasses the use of a wide variety of resins. As will be appreciated by the person skilled in the art, selection of resins takes into account both the chemical and physical performance of the resin. The resin will typically show selectivity for removing the desired metal ion from solution. The resin will also desirably have mechanical properties that limit or minimise attrition of the resin. In some instances, the mechanical strength of the resin may be increased during manufacture of the resin. In some instances, this may adversely impact on the chemical performance or selectivity of the resin.

The selectivity, loading capacity and elution characteristics of the resin may be tailored to the type and concentration of both the soluble value and the soluble non-value constituents of the solution and/or slurry being processed. In some instances the selectivity of the resin is simply controlled by the operating pH so that it is possible to separate out the desired metal(s) by a relatively simple pH control procedure. In some instances it may be preferable to use a resin that selectively and irreversibly loads a non-value impurity component ahead of the main ion exchange circuit where the soluble value metals are separated and ultimately recovered.

The particle size of the resin may suitably have a narrow size range. This is desirable as it allows for efficient separation of the resin from the solution or pulp or slurry.

In embodiments where soluble iron removal is required and achieved by pH adjustment it may be necessary to oxidise any ferrous iron to the ferric state in order to induce precipitation of the soluble iron. In such cases, mechanically agitated mixers may be supplemented with a suitable air/slurry contactor system to facilitate the oxidation of ferrous iron to the ferric state.

Subsequent to resin contact with the screened solution and/or pulp that represents the metal loading stage, in some embodiments, the loaded resin is separated from the treated solution and/or pulp by use of one or more screens. The selection of the optimum resin sizing and resin particle size distribution may be such as to maximise recovery of the loaded resin while at the same time minimising the energy and water washing requirements. If the resin screen size is too large, excessive amounts of loaded resin are lost out of the circuit. If the resin screen size is too small, excessive amount of solids will be recovered along with the loaded resin, leading to a much high level of water washing being required.

In embodiments of the present invention, transfer of the resin may be achieved using dense phase hydraulic conveying. One example of a suitable dense phase hydraulic conveying process is described in European patent number 0129999, the entire contents of which are here incorporated by cross reference.

In other embodiments, transfer of the resin may be achieved using water eduction, low shear recessed impellers, or peristaltic pumps.

The selection of the transfer method may depend upon the volume of resin required to be transferred. It may be desirable to keep the percentage of resin solids in the solution or pulp below 50%, or even below 40%, in order to minimise attrition during transfer. However, many resin in pulp systems face water balance issues and consequently resin transfer using large volumes of water is undesirable. However, transferring the resins using large volumes of water and recovering or recycling the water in a closed or partially closed loop enables the resin to be transferred as a relatively low percentage solids slurry without impacting on the water balance of the main processing plant.

In some embodiments of the present invention, various steps in the process, such as washing and/or elution, may be conducted such that there is an upflow of water or solution which causes fluidisation or entrainment of the resin in the upflowing liquid. This allows the resin to overflow from a process vessel over a screen to effect separation of the resin from the liquid. This also allows transfer of the resin to the next stage in the process without necessarily having to pass through a pump or pumps, which further minimises attrition of the resin. However, in some embodiments, it may be necessary to use pumps to transfer the resin. Alternatively, water eduction may be used to transfer the resin.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a process flow sheet of an embodiment of the present invention;

FIG. 2 shows a flow sheet of a single resin type, split elution circuit in accordance with an embodiment of the present invention; and

FIG. 3 shows a flow sheet of a two resins, split elution circuit in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

The following description of a presently preferred but non-limiting embodiment of the invention refers to the overall process outlined in FIG. 1. For convenience, this Figure is of a generic nature and all those skilled in the art will understand and acknowledge that there are a number of variations possible that comply with the overall concept of the invention. For example and for convenience purposes only, FIG. 1 is limited to the treatment and recovery of a single target metal by means of a single resin and a single elution stage with a single eluant.

The metal-bearing solution or slurry [1] is pumped by conventional means [2] to a pre-screening stage [3] where any oversize material is removed as waste [4]. Optionally, a suitable neutralising/pH control reagent [5] which may or may not be supplemented by air sparging to induce oxidation of ferrous iron to the ferric state, may be added directly to the metal-bearing solution or slurry [1] and/or as the metal-bearing solution or slurry is pumped to the pre-screening stage [2] and/or at the pre-screening stage [3] and/or as the pre-screened metal bearing solution or slurry is conveyed to the RIS/RIP circuit [10] and/or at the RIS/RIP circuit [7].

Recycled resin [6] is added to the RIS/RIP circuit [7] by means of a wet dense phase conveying system [8] together with any resin make-up requirement [9], the pre-screened and optionally pH adjusted feed solution or slurry [10], and any neutralising/pH control reagent [5] required to maximise loading of the target metal onto the selected resin. Mixing of the resin with the incoming solution or slurry and any neutralising/pH control reagent is achieved via mechanical methods supplemented by air sparging for oxidation of ferrous iron to the ferrous state if required.

The RIS/RIP circuit [7] may be designed and operated in conventional sequential column, fluidised bed or carousel modes, the choice depending to a large extent on volume flows, loading and eluting kinetics, and solids densities.

Following completion of the loading cycle, the metal-loaded resin and the depleted solution or pulp [11] are transferred to the loaded resin screening stage [12]. The screened loaded resin [13] is transferred by means of the wet dense phase conveying system [8] to the resin washing stage [14] and then to the resin elution stage [13] where the loaded, washed resin is contacted with the appropriate eluent [15]. The metal-rich eluate [16] is forwarded to the metal recovery circuit [17].

The eluted, metal-free resin [18] is transferred by means of wet dense phase conveyance system [8] to the resin transfer system [6] for ultimate transfer to the RIS/RIP circuit [7].

The metal-depleted solution or pulp [19] exiting the loaded resin screening stage [12] is treated by a combination of steps [20] for the safe disposal of all solids and solutions and comprises of appropriate neutralisation and solid/liquid separation stages.

FIG. 2 shows a flow sheet of a single resin type, split elution circuit in accordance with an embodiment of the present invention. In the embodiment shown in FIG. 2, a leach liquor containing dissolved metals (for example, containing dissolved copper, nickel and cobalt) is fed via line 100 to the first of a series of contacting vessels in which the leach liquor is contacted with a resin. These contacting vessels are denoted by reference numerals 102, 104, 106, 108, 110 and 112. The resin and liquor are contacted with each other in counter current flow.

In the embodiments shown in FIG. 2, the contacting circuit is effectively divided into two stages. The first stage includes vessels 102, 104 and 106. Regenerated resin from first elution column 114 is fed to contacting vessel 106 via line 116. The resin is transferred from the vessel 106 to vessel 104 via dense phase hydraulic conveying apparatus 118. Similarly, the resin is transferred from vessel 104 to vessel 102 by dense phase hydraulic conveying apparatus 120. Further, the resin from vessel 102 is transferred to the elution column 114 via dense phase hydraulic conveying apparatus 122. Use of dense phase hydraulic conveying apparatus to transfer the resin assists in minimising attrition of the resin.

The leach liquor 100 is initially fed to vessel 102. Liquor overflow from vessel 102 is transferred to vessel 104. Similarly, liquor overflow from vessel 104 is transferred to vessel 106.

A neutralising agent, such as a limestone slurry, is fed to respective vessels 102, 104, 106 by respective lines 124, 126, 128. Each vessel 102, 104, 106 is also provided with a low speed and/or low shear agitator 130, 132, 134, respectively. The agitators ensure good mixing and contact between the liquor and the resin whilst also maintaining the pulp in suspension. At the same time, due to the design and speed of the agitators, attrition of the resin is minimised.

The loaded resin leaving vessel 102 is transferred via line 103 to the first elution column 114. In this column, acid 136 is mixed with the resin to selectively elute the metal loaded onto the resin. In the example given in FIG. 2, copper is loaded onto the resin in vessels 102, 104, 106 by controlling the pH to between 2.5 and 3.5 and utilising a resin that selectively takes up copper from solution in that pH range.

By virtue of the operating conditions in vessels 102, 104, 106, the liquor 138 leaving vessel 106 is depleted in copper but still contains nickel and cobalt. Liquor 138 is fed to vessel 108 and thereafter to vessels 110 and 112. Resin (either regenerated or fresh resin) is fed via line 140 to vessel 112 and thereafter by respective dense phase hydraulic conveying apparatus 144, 146 (respectively) to vessel 110 and then to vessel 108. Loaded resin is transferred via dense phase conveying apparatus 148 to second elution column 150.

A neutralising agent, such as a limestone slurry, is fed via respective lines 152, 154, 156 to each of the vessels 108, 110, 112, respectively. The pH conditions in vessels 108, 110, 112 are such that nickel and cobalt are selectively taken up by the resin. For example, the pH may be controlled to fall within the range of 3.5 to 4.5. Thus, the loaded resin that is fed via line 158 to second elution column 150 is loaded with copper and nickel. The elution conditions in elution column 150 are such that nickel and cobalt are edited from the resin.

FIG. 3 shows a flow sheet of a two resins—split elution circuit. In FIG. 3, an acidic leach liquor 200 containing dissolved copper, nickel and cobalt is fed to the first stage of a metals recovery circuit. The first stage comprises contacting vessels 202, 204, 206 and 208. In each of these vessels, a first resin is contacted in counter current fashion using similar dense phase hydraulic conveying apparatus as described with reference to FIG. 2. For brevity of description, this need not be described further. Similarly, the liquor overflows each upstream vessel into a downstream vessel in a manner similar to that described with reference to FIG. 2. Again, for brevity of description, this need not be described further. Low speed agitators are provided in each vessel to maintain the slurry in suspension and to minimise attrition. A neutralising agent is fed to each vessel via respective lines 210, 212, 214, 216.

In the first stage, a resin that selectively removes one of the metals in solution is used. For example, iminodiacetic resin, which shows a good uptake of copper, a reasonable uptake of nickel and a poor uptake of cobalt may be used, with the pH conditions in the first stage being such that copper is selectively taken up by the resin. Thus, the loaded resin provided via line 218 to elution column 220 is loaded with copper. Acid supplied via line 222 is used to elute the copper from the resin and to regenerate the resin.

The liquor 224, that is depleted in copper, is fed to the second part of the process, which comprises contacting vessels 230, 232. In the second part, a resin that shows a good uptake of nickel and copper is used to remove the nickel and copper from the liquor.

Again, dense phase hydraulic conveying is used to transfer the resin. Again, low speed agitators that minimise attrition of the resin are used. Again, a neutralising agent is fed to the respective vessels in the second part via lines 226, 228.

The resin that is used in the second stage of the process may comprise bospicolyamine resin. This resin exhibits a very strong uptake of copper (indeed, so strong that copper is difficult to remove from this resin). However, in the process shown in FIG. 3, copper has been removed in the first stage of the process. This resin also shows a good uptake of nickel and cobalt, thus making it suitable for use in removing those metals from solution in the second stage. This resin is an expensive resin. Therefore, it is used for residual nickel and cobalt recovery after copper has been selectively removed from the liquor in the first stage of the process.

The loaded resin from vessel 230 is fed via line 234 to elution column 236. In elution column 236, the loaded resin is contacted with acid 238 to cause elution of the nickel and cobalt from the resin and to form a regenerated resin. The regenerated resin is transferred via line 240 back to vessel 232.

Although not shown in either FIG. 2 or FIG. 3, makeup resin may be provided in order to maintain resin balance in light of losses of resin.

The eluted metal streams may be treated to recover metal therefrom using any process is known to be suitable for that use.

In some embodiments of the present invention, the following advantages may arise:

-   -   enhanced efficiency of the RIP and RIS processes by means of         improved design and operating procedures involved in the         contacting, transfer, handling and elution of the resins.     -   enhanced efficiency of the RIP and RIS processes by means of the         use of specific designs and types of pump suitable for resin         transfer to minimise resin attrition, as described herein above.     -   enhanced efficiency of the RIP and RIS processes by means of the         use of specific designs, types and speed of agitators/mixers         required for efficient mixing and suspension of the resin while         minimising resin attrition, as described herein above.     -   enhanced efficiency of the RIP and RIS processes by means of the         use of specific designs of air mixing of the resin with the pulp         or solution that also assists in the oxidation of ferrous iron         to the ferric state where it is required or desirable to remove         iron in conjunction with pH control. For example, many         processing circuits, such as base metals tails neutralisation,         contain residual metal values. In the case of acidic pulp tails,         a significant portion of iron is also typically present. Iron         can be precipitated from solution as either ferric (Fe³⁺) or         ferrous (Fe²⁺) hydroxide. Ferrous hydroxide does not form a         dense, easy to settle/dewater solid precipitate and therefore         acidic tail solutions being neutralised are frequently aerated         using air or oxygen sparging to convert ferrous to ferric and         preferentially precipitate ferric hydroxides. pH control is also         used to assist in achieving precipitation of ferric hydroxides.         Air mixing resin in circuits causes less attrition compared with         mechanical agitation but air mixing is an expensive operating         cost and most plants now use mechanical mixing rather than air         mixing. However, in embodiments of the present invention where         it is designed to convert ferrous to ferric as part of the         process, the present invention envisages that the air sparging         and design of the contactor can be modified to achieve both         duties, i.e. ferrous to ferric conversion and air mixing of the         resin with the pulp.     -   enhanced efficiency of the RIP and RIS processes by means of         improved design and operating procedures involved in the         screening processes to remove any oversize material in the         original feed pulp and/or feed solution and/or any solid         neutralising agent used for pH control purposes.     -   enhanced efficiency of the RIP and RIS processes by means of pH         control prior to and during the processes to maximise the         loading capacity and/or the selectivity and/or elution of the         resin.     -   enhanced efficiency of the RIP and RIS processes by means of pH         control prior to and during the processes to eliminate         non-target metals through precipitation mechanisms.     -   enhanced efficiency of the RIP process by means of improved         methods of introduction of resin to viscous RIP circuits to         ensure adequate resin mixing within the pulp and avoid resin         floating and/or short circuiting.     -   enhanced efficiency of the RIP and RIS processes by means of an         improved resin transfer system which allows water to be used to         fluidise the resin enabling its efficient transfer while         minimising resin losses through attrition while at the same time         ensuring that resin transfer can be accomplished with minimal         effect on circuit water balance.     -   enhanced efficiency of the RIP and RIS processes when used to         treat complex feed pulps and solutions containing two or more         soluble target metals by means of using a single resin in the         circuit but changing the pH across different stages of the         circuit to optimise the uptake/removal and recovery of different         target metals.     -   enhanced efficiency of the RIP and RIS processes when used to         treat complex feed pulps and solutions containing two or more         soluble target metals by means of using more than one type of         resin to separate and remove each of the soluble target metals         independently of the other soluble target metals. In one         preferred embodiment the two or more types of resin may be         contained within separate columns. In another preferred         embodiment the two or more types of resin may be mixed together         and contained within the same column or columns     -   enhanced efficiency of the RIP and RIS processes by means of         appropriate temperature control of the incoming feed pulps or         solutions and/or of the resin columns in their loading and/or         washing and/or eluting duties.

In the preceding description of the invention and in the claims which follow, except where the context requires otherwise due to express language or necessary implication, the words “comprise” or variations such as “comprises” or “comprising” are used in an inclusive sense, i.e., specify the presence of stated features, but not preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that in this invention the preferred embodiments are not limited to those particular materials described, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention in any way.

It is to be noted that, as used herein, the singular forms of “a”, “an” and “the” include the plural unless the context clearly requires otherwise. Unless defined otherwise, all technical and scientific terms herein have the same meanings as commonly understood by one of ordinary skill in the art to which the invention belongs. 

1. A process for the treatment of solutions or slurries containing dissolved metals comprising the steps of: a) contacting the solution or slurry with an ion exchange resin that selectively removes one or more dissolved metals from the solution or slurry, said contacting comprising introducing the solution or slurry and the resin into a vessel or column, wherein the resin is introduced into the vessel or column via sub-surface means, b) separating loaded resin from the solution or slurry; c) eluting the one or more metals from the loaded resin with an eluting agent; d) separating the eluting solution containing eluted metal ions from the resin; and e) transferring regenerated resin from step (d) back to step (a).
 2. A process as claimed in claim 1 further comprising washing the loaded resin to remove entrained solids, solution or slurry prior to step (c);
 3. A process as claimed in claim 1 wherein the slurry or solution is subjected to a pre-treatment that removes oversize particles and other contaminants therefrom prior to contacting or mixing the slurry or solution with the resin.
 4. A process as claimed in claim 3 wherein the pre-treatment step comprises screening, settling, sedimentation, clarification, separation using hydrocyclones, or centrifuging.
 5. A process as claimed in claim 1 wherein a low speed or a low shear mechanical mixer is used to mix the resin with the solution or slurry.
 6. A process as claimed in claim 5 wherein the low speed mechanical mixer has an agitator operated such that a tip speed of the agitator is less than 4.0 m/sec.
 7. A process as claimed in claim 6 wherein the tip speed of the agitator is less than 3.8 m/sec.
 8. A process as claimed in claim 1 wherein the solutions or slurries are treated by addition of one or more reagents to adjust pH of the solutions or slurries to ensure that the target metal(s) remain in solution while at the same time ensuring that the ion exchange resin is operating within its optimal pH range for metal uptake and to remove potentially interfering non-target soluble metal ions by in-situ precipitation, wherein precipitation of the non-target soluble metal ions occurs in a vessel in which step (a) takes place.
 9. A process as claimed in claim 8 wherein the non-target soluble metal comprises ferric ions and the process comprises adjusting the pH in step (a) to a value in the range of about 2.8 to 3.8.
 10. A process as claimed in claim 8 wherein pH adjustment is achieved by adding a solid neutralising agent to the solution or slurry and the solid neutralising agent is screened to remove oversize particles having a particle size greater than a predetermined size prior to mixing with the ion exchange resin.
 11. A process as claimed in claim 8 wherein pH adjustment is achieved by adding a solid neutralising agent to the solution or slurry and the solid neutralising agent is treated to remove oversize particles having a particle size greater than a predetermined size prior to mixing with the solution or slurry.
 12. A process as claimed in claim 1 wherein the particle size of the resin has a narrow size range.
 13. A process as claimed in claim 1 wherein soluble iron removal from the solution or slurry is required and is achieved by pH adjustment and ferrous iron is oxidised to the ferric state in order to induce precipitation of the soluble iron, wherein an air/slurry contactor system is provided to facilitate oxidation of ferrous iron to the ferric state.
 14. A process as claimed in claim 1 wherein subsequent to resin contact with the solution and/or slurry, the loaded resin is separated from the treated solution and/or pulp in step (b) by use of one or more screens.
 15. A process as claimed in claim 1 wherein transfer of the resin is achieved using dense phase hydraulic conveying.
 16. A process as claimed in claim 1 wherein transfer of the resin is achieved using water eduction, low shear recessed impellers, or peristaltic pumps.
 17. A process as claimed in claim 1 wherein the percentage of resin solids in the solution or slurry is below 50%.
 18. A process as claimed in claim 17 wherein the percentage of resin solids in the solution or slurry is below 40%.
 19. A process as claimed in claim 1 wherein the resin is transferred in water and the process further comprises recovering or recycling the water in a closed or partially closed loop.
 20. A process as claimed in claim 1 wherein washing and/or elution is conducted such that there is an upflow of water or solution which causes fluidisation or entrainment of the resin in the upflowing liquid.
 21. A process as claimed in claim 20 wherein the resin overflows from a process vessel over a screen to effect separation of the resin from the liquid.
 22. A process as claimed in claim 20 wherein transfer of the resin to a next stage in the process occurs without passing the resin through a pump or pumps. 